Avian Bornavirus (ABV) is a serious infectious agent that poses a significant threat to various avian species, particularly parrots (psittacine family). This single-strand RNA virus is a neurotropic pathogen that preferentially targets the bird’s nervous system. Its discovery in 2008 confirmed the cause of a devastating, long-recognized condition. Historically, this infection was associated with Proventricular Dilatation Disease (PDD), first described in the 1970s as “macaw wasting disease.” Avian Bornavirus now encompasses a genetically diverse group of viruses responsible for this chronic and often fatal illness in captive birds.
Recognizing Symptoms and Proventricular Dilatation Disease
Bornavirus infection leads to a wide range of clinical outcomes, categorized into digestive and neurological presentations. PDD, the physical manifestation, involves a severe inflammatory response (ganglioneuritis) in the peripheral nerves regulating the gastrointestinal tract. This inflammation damages the nerves controlling the muscles of the proventriculus (glandular stomach) and gizzard, resulting in slow or absent movement of food.
The resulting lack of muscle function causes food to accumulate, severely enlarging or dilating the proventriculus. Affected birds often exhibit progressive weight loss despite a normal or increased appetite. The inability to properly digest and absorb nutrients leads to emaciation and the passage of undigested food in the feces.
Digestive signs also include regurgitation, vomiting, and chronic crop stasis. The clinical presentation is highly variable, and not all birds display classic gastrointestinal signs. Some infected birds primarily develop neurological deficits, which may occur with or without digestive issues.
Neurological symptoms arise when the virus targets the central nervous system, causing encephalitis. Owners may observe ataxia (loss of full control of bodily movements), leading to uncoordinated walking or perching. Other common signs include head tremors, generalized weakness, and, in severe cases, seizures. The presence of these signs warrants immediate consultation with an avian veterinarian.
How Bornavirus Spreads and Targets the Body
Avian Bornavirus is highly contagious, primarily transmitted through the fecal-oral route. Viral particles are shed intermittently in droppings, oral secretions, and urine. Birds become infected by ingesting contaminated food, water, or bedding material.
Aerosol transmission through respiratory droplets is also suspected. Furthermore, vertical transmission is possible, where an infected female bird passes the virus directly to her offspring through the egg.
The virus establishes a persistent infection by targeting the nervous system, including the enteric nervous system (ENS) lining the digestive tract. Targeting nerve ganglia within the gut wall causes the functional damage seen in PDD. The resulting inflammation interferes with nerve signals required for normal peristalsis, leading to gastrointestinal paralysis.
A notable feature of ABV infection is latency and asymptomatic carriage. Many birds that test positive may never develop clinical signs of PDD, remaining asymptomatic carriers for years. These infected birds can still shed the virus intermittently, acting as a reservoir of infection. The incubation period is highly variable, ranging from a few weeks to many years.
Testing Methods and Long-Term Care
Diagnosing Avian Bornavirus infection in a live bird requires a multi-faceted approach due to intermittent shedding patterns. Antemortem testing involves two main types of laboratory analysis: direct viral detection and serology. Polymerase Chain Reaction (PCR) testing detects viral RNA, often performed on samples like feces, cloacal swabs, or crop swabs.
The limitation of PCR is that intermittent viral shedding can lead to false-negative results if the bird is not actively shedding. Serology detects antibodies against ABV in the blood, indicating past exposure or current infection. A bird positive for antibodies but negative for viral RNA is considered an asymptomatic carrier.
The definitive diagnosis of PDD relies on histopathology, typically a post-mortem examination of tissue. This method identifies characteristic lymphoplasmacytic infiltrates (inflammatory cell clusters) in the nerve ganglia of the proventriculus. For live birds with strong clinical suspicion, a biopsy of the crop or proventriculus may be performed to look for these lesions.
There is currently no cure for ABV infection, so long-term care focuses on managing symptoms and providing supportive therapy. Management includes dietary adjustments, such as using easily digestible, high-calorie foods to maximize nutrient absorption. Reducing environmental stress is also an important component of care.
Veterinarians may prescribe non-steroidal anti-inflammatory drugs (NSAIDs), such as Celecoxib, to help reduce the neuro-inflammation underlying the disease. While these medications improve quality of life, they do not eliminate the virus. Strict biosecurity measures are paramount for bird owners, including isolating any newly acquired or infected birds to prevent spread.